1. Field of the Invention
The present invention relates to a microwave device intended for the treatment of process liquids, preferably the labelling of precursors to radiopharmaceuticals. The invention also relates to a method for treating process liquids, preferably when labelling precursors to radiopharmaceuticals with the aid of microwave radiation.
2. Description of the Prior Art
In certain cases, treatment with microwaves is able to increase drastically the rates of organic reactions. See in this respect R. Gedye et al, Tetrahedron Letters, 27 279 (1986). Microwaves have also been earlier used for the preparation of positron-emitting precursors that are intended for labelling purposes; see R.a. Ferrieri et al, Int. J. Appl. Radiat. Isot. 34 897 (1983). Microwaves have also been used in the preparation of radiopharmaceuticals labelled with .sup.11 C and .sup.18 F. Such microwave treatment processes result in short reaction times and higher yields of the radio-labelled product. The microwave device used in the aforesaid liquid reactions is a conventional domestic microwave oven. An oven of this kind normally has a microwave frequency of 2450 MHz.
In the preparation of radiopharmaceuticals, there is used an accelerator for the preparation of radioactive isotopes which are formed into larger molecules in a subsequent radiochemical process and later administered to the patient, who is subsequently examined with a positron camera. The normal half-life of the isotopes is from 2 minutes to about 110 minutes. It will be realized that the radiochemical process must be capable of being carried out quickly, in view of the short half-life of the isotopes.
The microwave field can be described as a periodically reversed electromagnetic field. The electrons in the polar molecules follow the field direction and are placed in periodic motion, which in turn results in the generation of heat, among other things.
The drawbacks with the use of the aforesaid microwave oven when treating precursors to radiopharmaceuticals are that the microwave field cannot be adapted either to the type or to the quantity of the process liquid to be treated. The geometry of the oven is determined once and for all, and the microwave field can neither be concentrated nor varied with respect to strength and frequency.